Testing apparatus and method for testing analog-to-digital converter

ABSTRACT

The invention provides a testing apparatus. In one embodiment, the testing apparatus receives a plurality of bit signals output by an analog-to-digital converter, and comprises a plurality of frequency counters and a comparison module. The frequency counters respectively calculate a plurality of transition frequencies of the values of the bit signals. The comparison module respectively compares the transition frequencies with a plurality of ideal transition frequencies to obtain a plurality of error frequencies. The performance analysis module estimates a performance value of the analog-to-digital converter according to the error frequencies.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of Taiwan Patent Application No.100146406, filed on Dec. 15, 2011, the entirety of which is incorporatedby reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to analog-to-digital converters, and moreparticularly to testing of analog-to-digital converters.

2. Description of the Related Art

Analog-to-digital converters convert analog signals to digital signals.Because a digital signal processor can only receive a digital signal asan input, an analog-to-digital converter is often used to convert ananalog signal to a digital signal for input of the digital signalprocessor. If the analog-to-digital signal is poor, errors are inducedin the input signal of the digital signal processor, and performance ofthe digital signal processor is degraded. The evaluation of theperformance of analog-to-digital converters is therefore important toweed out poor analog-to-digital converters.

Ordinarily, testing of analog-to-digital converters are performed duringthe manufacturing stage of the analog-to-digital converters. A testingapparatus is used to perform testing of analog-to-digital converters.Referring to FIG. 1, a block diagram of a testing apparatus 100 fortesting an analog-to-digital converter 190 is shown. Theanalog-to-digital converter 190 receives an analog input signal and thenconverts the analog input signal to a plurality of bit signals bit0,bit1, . . . , and bit9. The testing apparatus 100 then receives the bitsignals and then gives a performance value to the analog-to-digitalconverter 190 according to the bit signals. In one embodiment, thetesting apparatus 100 comprises a decimal converter 110, a histogramgenerator 120, and a performance analyzer 130.

The decimal converter 110 converts the binary bit signals bit0, bit1,bit2, . . . , bit9 into a series of decimal values. The histogramgenerator 120 then generates a histogram according to the decimalvalues. The performance analyzer 130 then estimates an integralnonlinearity (INL) value and a differential nonlinearity (DNL) valueaccording to the histogram to determine the performance of theanalog-to-digital converter 190. FIG. 2A shows an analog input signalreceived by the analog-to-digital converter 190, and FIG. 2B shows ahistogram generated by the histogram generator 120 according to thedecimal values.

The testing apparatus 100 shown in FIG. 1, however, has a highmanufacturing cost and a complicated circuit design. First, to store thedecimal values generated by the decimal converter 110, the histogramgenerator 120 must comprise a memory with a large memory space whichincreases the hardware cost of the testing apparatus 100. In addition,the histogram generator 120 and the performance analyzer 130 needcomplicated circuits to implement complex calculations, and thisincreases the hardware cost of the testing apparatus 100. To reduce thehardware cost of the testing apparatus, a testing apparatus with asimplified circuit structure for testing an analog-to-digital converteris required.

BRIEF SUMMARY OF THE INVENTION

The invention provides a testing apparatus. In one embodiment, thetesting apparatus receives a plurality of bit signals output by ananalog-to-digital converter, and comprises a plurality of frequencycounters and a comparison module. The frequency counters respectivelycalculate a plurality of transition frequencies of the values of the bitsignals. The comparison module respectively compares the transitionfrequencies with a plurality of ideal transition frequencies to obtain aplurality of error frequencies. The performance analysis moduleestimates a performance value of the analog-to-digital converteraccording to the error frequencies.

The invention provides a method for testing an analog-to-digitalconverter. In one embodiment, a testing apparatus comprises a pluralityof frequency counters, a comparison module, and a performance analysismodule. First, a plurality of bit signals output by an analog-to-digitalconverter is received. A plurality of transition frequencies of thevalues of the bit signals are then calculated by the frequency counters.The transition frequencies are then compared with a plurality of idealtransition frequencies by the comparison module to obtain a plurality oferror frequencies. A performance value of the analog-to-digitalconverter is then estimated by the performance analysis module accordingto the error frequencies.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a block diagram of a conventional testing apparatus fortesting an analog-to-digital converter;

FIG. 2A shows an analog input signal received by an analog-to-digitalconverter;

FIG. 2B shows a histogram generated by a histogram generator accordingto decimal values;

FIG. 3 is a block diagram of a testing apparatus for testing ananalog-to-digital converter according to the invention;

FIG. 4 is a flowchart of a method for testing an analog-to-digitalconverter according to the invention;

FIG. 5 is a schematic diagram of an embodiment of a relationship betweena plurality of bit signals and corresponding transition frequencies;

FIG. 6A is a schematic diagram of ideal values of a plurality of bitsignals generated by an ideal analog-to-digital converter;

FIG. 6B is a schematic diagram of real values of a plurality of bitsignals generated by a real analog-to-digital converter;

FIG. 7 is a schematic diagram of a relationship between ideal values andreal values of transition frequencies of bit signals according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

Referring to FIG. 3, a block diagram of a testing apparatus 300 fortesting an analog-to-digital converter 390 according to the invention isshown. The analog-to-digital converter 390 receives an analog inputsignal and converts the analog input signal to a plurality of bitsignals S₀, . . . , S₇, S₈, and S₉. The bit signals S₀, . . . , S₇, S₈,and S₉ are bit values bit0, . . . , bit7, bit8, bit9 generated by theanalog-to-digital converter 390 by converting the analog input signalfrom analog to digital. In one embodiment, the analog input signalreceived by the analog-to-digital converter 390 is a triangle wave or aramp wave.

The testing apparatus 300 receives a plurality of bit signals S₀, . . ., S₇, S₈, and S₉ output by the analog-to-digital converter 390, andestimates a performance value of the analog-to-digital converter 390according to the bit signals S₀, . . . , S₇, S₈, and S₉. In oneembodiment, the testing apparatus 300 comprises a plurality of low passfilters 310˜319, a plurality of frequency counters 320˜329, a comparisonmodule 330, and a performance analysis module 340. The low pass filters310˜319 filter the bit signals S₀, . . . , S₇, S₈, and S₉ output by theanalog-to-digital converter 390 to generate a plurality of filtered bitsignals S₀′, . . . , S₇′, S₈′, and S₉′. In one embodiment, the low passfilters 310˜319 respectively averages every three bits of the bitsignals S₀, . . . , S₇, S₈, and S₉ to obtain the filtered bit signalsS₀′, . . . , S₇′, S₈′, and S₉′. In another embodiment, the low passfilters 310˜319 respectively averages every four bits of the bit signalsS₀′, . . . , S₇, S₈, and S₉ to obtain the filtered bit signals S₀′, . .. , S₇′, S₈′, and S₉′.

The frequency counters 320˜329 respectively calculate transitionfrequencies of values of the filtered bit signals S₀′, . . . , S₇′, S₈′,and S₉′ to obtain a plurality of transition frequencies F₀, . . . , F₇,F₈, and F₉. In one embodiment, the frequency counters 320˜329respectively calculates a plurality of first total frequencies f1, . . ., f7, f8, f9 of transitions from the value 0 to the value 1 of thefiltered bit signals S₀′, . . . , S₇′, S₈′, and S₉′, then calculates aplurality of second total frequencies f1′, . . . , f7′, f8′, f9′ oftransitions from the value 1 to the value 0 of the filtered bit signalsS₀′, . . . , S₇′, S₈′, and S₉′, and then respectively adds the secondtotal frequencies to the first total frequencies to obtain thetransition frequencies F₀, . . . , F₇, F₈, and F₉.

The comparison module 330 receives the transition frequencies F₀, . . ., F₇, F₈, and F₉ generated by the frequency counters 320˜329. Thecomparison module 330 then compares the transition frequencies F₀, . . ., F₇, F₈, and F₉ with ideal transition frequencies F₀′, . . . , F₇′,F₈′, and F₉′ to obtain a plurality of error frequencies E₀, . . . , E₇,E₈, and E₉. In one embodiment, the comparison module 330 subtracts thetransition frequencies F₀, . . . , F₇, F₈, and F₉ from the idealtransition frequencies F₀′, . . . , F₇′, F₈′, and F₉′ to obtain theerror frequencies E₀, . . . , E₇, E₈, and E₉. The performance analysismodule 340 then estimates a performance value of the analog-to-digitalconverter 390 according to the error frequencies E₀, . . . , E₇, E₈, andE₉. In one embodiment, the performance analysis module 340 averages theerror frequencies E₀, . . . , E₇, E₈, and E₉ according to a weight toobtain the performance value. When the error frequencies E₀, . . . , E₇,E₈, and E₉ are high, the performance value is high, and the performancevalue of the analog-to-digital converter 390 is low.

Because the testing apparatus 300 calculates the transition frequenciesof the bit signals S₀, . . . , S₇, S₈, and S₉ with the frequencycounters 320˜329 output by the analog-to-digital converter 390, and thenestimates the performance of the analog-to-digital converter 390according to the transition frequencies, the testing apparatus 300 doesnot require a memory with a large memory space for storing the values ofbit signals S₀, . . . , S₇, S₈, and S₉ as the conventional testingapparatus 100 shown in FIG. 1 does. The hardware cost of the testingapparatus 300 is therefore lower than that of the testing apparatus 100shown in FIG. 1. In addition, the circuit design of the frequencycounters 320˜329, the comparison module 330, and the performanceanalysis module 340 is simple, and the hardware cost of the testingapparatus 300 is further reduced. The testing apparatus 300 thereforehas a lower hardware cost than that of the testing apparatus 100 shownin FIG. 1.

Referring to FIG. 4, a flowchart of a method 400 for testing ananalog-to-digital converter according to the invention is shown. First,a triangle wave is sent to an analog-to-digital converter 390 as aninput (step 402). The testing apparatus 300 then receives a plurality ofbit signals S₀, . . . , S₇, S₈, and S₉ output by the analog-to-digitalconverter 390 (step 404). The testing apparatus 300 then filters the bitsignals S₀, . . . , S₇, S₈, and S₉ with low pass filters 310˜319 toobtain a plurality of filtered bit signals S₀′, . . . , S₇′, S₈′, andS₉′ (step 406). The testing apparatus 300 then calculates a plurality oftransition frequencies of the values of the filtered bit signals S₀′, .. . , S₇′, S₈′, and S₉′ with a plurality of frequency counters 320˜329to obtain a plurality of transition frequencies F₀, . . . , F₇, F₈, andF₉ (step 408). The comparison module 330 then compares the transitionfrequencies F₀, . . . , F₇, F₈, and F₉ with a plurality of idealtransition frequencies to obtain a plurality of error frequencies E₀, .. . , E₇, E₈, and E₉ (step 410). The performance analysis module 340then calculates a performance value of the analog-to-digital converter390 according to the error frequencies E₀, . . . , E₇, E₈, and E₉ (step412). In one embodiment, when any of the error frequencies which do notcorrespond to the three least significant bits are positive, theperformance analysis module 340 determines the performance value of theanalog-to-digital converter 390 to have failed to pass the thresholdlevel.

Referring to FIG. 5, a schematic diagram of an embodiment of arelationship between a plurality of bit signals and correspondingtransition frequencies is shown. Assume that the analog-to-digitalconverter 390 outputs 10 bit signals S_(o), . . . , S₇, S₈, and S₉respectively corresponding to the bit0, . . . , bit7, bit8, bit9 shownin FIG. 5, wherein the bit 0 is a least significant bit (LSB), and thebit 9 is a most significant bit (MSB). Assume that the testing apparatus300 receives samples corresponding to 16 sample indexes from theanalog-to-digital converter 390. For example, the samples correspondingto the time index 10 are (0, 0, 0, 0, 0, 0, 1, 0, 0, 1), and the samplescorresponding to the time index 16 are (0, 0, 0, 0, 0, 0, 1, 1, 1, 1).The testing apparatus 100 shown in FIG. 1 converts the samplescorresponding to the sample index 10 to a decimal value of 9, convertsthe samples corresponding to the time index 16 to a decimal value of 15,and then estimates a performance value of the analog-to-digitalconverter according to the decimal values. The testing apparatus 100shown in FIG. 1 therefore has to store the decimal values in a memory,and the hardware cost of the testing apparatus 100 is thereforeincreased.

On the contrary, the testing apparatus 300 uses frequency counters320˜329 to calculate the transition frequencies of values of the bitsignals bit0˜bit9 from 0 to 1 or from 1 to 0. For example, thetransition frequencies of the bit signals bit0, bit1, bit2, and bit 3are respectively 15, 7, 3, and 0. The testing apparatus 300 thereforedoes not need a memory to store the values of the bit signals, and thehardware cost of the testing apparatus 300 is lowered. For example, thevalue of the bit signal bit1 changes from 0 to 1 at the sample indexes3, 7, 11, and 15, and the value of the bit signal bit1 changes from 1 to0 at the sample indexes 5, 9, and 13, and the transition frequencycorresponding to the bit signal bit1 is therefore 7. In addition, thevalue of the bit signal bit2 changes from 0 to 1 at the sample indexes 5and 13, and the value of the bit signal bit2 changes from 1 to 0 at thesample index 9, and the transition frequency corresponding to the bitsignal bit2 is therefore 3.

An ideal analog-to-digital converter does not generate noises and thebit signals generated by the ideal analog-to-digital converter haveideal values. Referring to FIG. 6A, a schematic diagram of ideal valuesof a plurality of bit signals generated by an ideal analog-to-digitalconverter is shown. The value corresponding to the least significant bitchanges at each sample index, and the value corresponding to the mostsignificant bit doesn't change during the sample indexes 1˜14. Thedecimal values corresponding to the sample indexes therefore graduallyincrease. A real analog-to-digital converter generates noises and thebit signals generated by the real analog-to-digital converter compriseerrors. Referring to FIG. 6B, a schematic diagram of real values of aplurality of bit signals generated by a real analog-to-digital converteris shown. The decimal values corresponding to the sample indexes do notregularly change due to errors induced by noises.

The errors comprised by the bit signals generated by the realanalog-to-digital converter shown in FIG. 6B lead to errors in thetransition frequencies F₀˜F₉ generated by frequency counters 320˜329.The low pass filters 310˜319 therefore filter the bit signals S₀˜S₉ toobtain filtered bit signals S₀′˜S₉′. Referring to FIG. 7, a schematicdiagram of a relationship between the ideal values and the real valuesof transition frequencies of bit signals according to the invention isshown. The ideal values of transition frequencies of bit signals S₀, S₁,S₂, . . . , S₉ generated by an ideal analog-to-digital converter arerespectively 4091, 2044, 1024, . . . , 4, as shown in the first row ofthe table of FIG. 7. The ideal values of transition frequencies offiltered bit signals S₀′, S₁′, S₂′, . . . , S₉′ generated by low passfilters by averaging every three bits of the bit signals arerespectively 4085, 2044, 1024, . . . , 4, as shown in the second row ofthe table of FIG. 7. The ideal values of transition frequencies offiltered bit signals S₀′, S₁′, S₂′, . . . , S₉′ generated by low passfilters by averaging every four bits of the bit signals are respectively5, 4, 1024, . . . , 4, as shown in the third row of the table of FIG. 7.

The real values of transition frequencies of bit signals S₀, S₁, S₂, . .. , S₉ generated by a real analog-to-digital converter are respectively2393, 2471, 1808, . . . , 12, as shown in the fourth row of the table ofFIG. 7. The real values of transition frequencies of filtered bitsignals S₀′, S₁′, S₂′, . . . , S₉′ generated by low pass filters byaveraging every four bits of the bit signals are respectively 583, 565,914, . . . , 4, as shown in the fifth row of the table of FIG. 7. Asshown in FIG. 5, because the low pass filters 310—319 filter the bitsignals S₀˜S₉, the real values of the transition frequencies of thefiltered bit signals S₀′ and S₁′ corresponding to the two leastsignificant bits greatly differ from the ideal values, and cannot beused as a reference for calculation of the performance value of theanalog-to-digital converter. The performance analysis module 340therefore only estimates the performance value of the analog-to-digitalconverter 390 according to the error frequencies E₉˜E₃ which does notcorrespond to the two least significant bits S₀ and S₁. For example, thereal values of the error frequencies E₀, E₁, and E₂ corresponding to theleast significant bits S₀, S₁, and S₂ differ from the ideal values.Thus, when the performance analysis module 340 finds that any of theerror frequencies E₃˜E₉ which does not correspond to the three leastsignificant bits are positive, the performance analysis module 340determines that the performance of the analog-to-digital converter 390has failed to pass a threshold level.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

What is claimed is:
 1. A testing apparatus, receiving a plurality of bitsignals output by an analog-to-digital converter, comprising: aplurality of frequency counters, respectively calculating a plurality oftransition frequencies of the values of the bit signals; a comparisonmodule, respectively comparing the transition frequencies with aplurality of ideal transition frequencies to obtain a plurality of errorfrequencies; and a performance analysis module, estimating a performancevalue of the analog-to-digital converter according to the errorfrequencies.
 2. The testing apparatus as claimed in claim 1, wherein theanalog-to-digital converter receives a triangle wave or a ramp wave, andconverts the triangle wave or the ramp wave from analog to digital togenerate the bit signals.
 3. The testing apparatus as claimed in claim1, wherein the combination of the plurality of bit values of the bitsignals corresponding to a single sample index is a binary value of aninput value of the analog-to-digital converter.
 4. The testing apparatusas claimed in claim 1, wherein the frequency counters respectivelycalculates a plurality of first total frequencies of transitions fromthe value 0 to the value 1 of the bit signals, calculates a plurality ofsecond total frequencies of transitions from the value 1 to the value 0of the bit signals, and adds the second total frequencies to the firsttotal frequencies to obtain the transition frequencies.
 5. The testingapparatus as claimed in claim 1, wherein the testing apparatus furthercomprises: a plurality of low pass filters, respectively coupled betweenthe analog-to-digital converter and one of the frequency counters,respectively filtering the bit signals to obtain a plurality of filteredbit signals, and then sending the filtered bit signals to the frequencycounters as the inputs of the frequency counters.
 6. The testingapparatus as claimed in claim 5, wherein the low pass filters averageeach three or four sample values of the bit signals to obtain the samplevalues of the filtered bit signals.
 7. The testing apparatus as claimedin claim 1, wherein if any of the error frequencies which does notcorrespond to the three least significant bits are positive, theperformance analysis module determines the performance value of theanalog-to-digital converter to have failed to pass the threshold level.8. The testing apparatus as claimed in claim 1, wherein the performanceanalysis module averages the error frequencies according to apredetermined weight to obtain the performance value, wherein a highperformance value indicates low performance of the analog-to-digitalconverter.
 9. The testing apparatus as claimed in claim 1, wherein theperformance analysis module estimates the performance value according tothe error frequencies which does not correspond to the two leastsignificant bits.
 10. A method for testing an analog-to-digitalconverter, comprising: receiving a plurality of bit signals output by ananalog-to-digital converter; calculating a plurality of transitionfrequencies of the values of the bit signals with a plurality offrequency counters; respectively comparing the transition frequencieswith a plurality of ideal transition frequencies by a comparison moduleto obtain a plurality of error frequencies; and estimating a performancevalue of the analog-to-digital converter by a performance analysismodule according to the error frequencies.
 11. The method as claimed inclaim 10, further comprising: generating a triangle wave or a ramp waveas an input signal of the analog-to-digital converter; wherein theanalog-to-digital converter converts the triangle wave or the ramp wavefrom analog to digital to generate the bit signals.
 12. The method asclaimed in claim 10, wherein the combination of the plurality of bitvalues of the bit signals corresponding to a single sample index is abinary value of an input value of the analog-to-digital converter. 13.The method as claimed in claim 10, wherein calculation of the transitionfrequencies comprises: respectively calculating a plurality of firsttotal frequencies of transitions from the value 0 to the value 1 of thebit signals; respectively calculating a plurality of second totalfrequencies of transitions from the value 1 to the value 0 of the bitsignals; and adding the second total frequencies to the first totalfrequencies to obtain the transition frequencies.
 14. The method asclaimed in claim 10, wherein the method further comprises: respectivelyfiltering the bit signals by a plurality of low pass filters to obtain aplurality of filtered bit signals; and sending the filtered bit signalsto the frequency counters as the inputs of the frequency counters. 15.The method as claimed in claim 14, wherein filtration of the bit signalscomprises: averaging each three or four sample values of the bit signalsby the low pass filters to obtain the sample values of the filtered bitsignals.
 16. The method as claimed in claim 10, wherein estimation ofthe performance value comprises: if any of the error frequencies whichdoes not correspond to the three least significant bits are positive,determining the performance value of the analog-to-digital converter bythe performance analysis module to have failed to pass the thresholdlevel.
 17. The method as claimed in claim 10, wherein estimation of theperformance value comprises: averaging the error frequencies accordingto a predetermined weight by the performance analysis module to obtainthe performance value; wherein a high performance value indicates lowperformance of the analog-to-digital converter.
 18. The method asclaimed in claim 10, wherein estimation of the performance valuecomprises: estimating the performance value by the performance analysismodule according to the error frequencies which does not correspond tothe two least significant bits.